Anne Heche was declared brain dead earlier this week after she crashed her car into a house.
The department said in a statement to the Associated Press that no further investigative efforts will be made in the case and that any records or information that have already been requested will be collected as a matter of formality.
If a suspect dies, the department doesn't give evidence to the district attorney.
The department said last week that they found a narcotic in a preliminary blood draw, though further testing would be needed.
Heche was declared brain dead on Friday after her family said she was unlikely to survive her injuries.
Heche remains on life support as a Los Angeles organ and tissue bank evaluates if she is a match for organ donation.
Heche crashed her Mini Cooper into a house in Los Angeles on August 5. It took 59 firefighters more than an hour to put out the fire. The homeowner's sons started a crowd funding page.
The investigation into Anne Heche's car crash has ended.